Means for heating blast furnace air



Aug. 10, 1965 F. J. KolNxs 3,199,849

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A T T ORNE'Y'.

United States Patent O 3,199,849 MEANS FR l-IEATING BLAST FURACE AER Frank l'. Kenis, Toledo, Ghia, asignar to Midland-Ross Corporation, Toiedo, hio, a corporation of @Mo Filed dan. 15, 1%3, Ser. No. 251,512 7 Claims. (Si. 263--19) The process of reducing iron ore to pig iron in a blast furnace requires the introduction of a continuous supply of preheated air into the blast furnace at a rapid rate. To provide the needed preheated air, each blast furnace is customarily provided with a plurality of regenerative heat exchange devices, called stoves. Generally, each blast furnace is provided with three stoves and older installations were frequently provided with four stoves. Each stove comprises a large perforated mass of refractory which is first heated by passing products of combustion therethrough and, after being heated, is used to heat cold blast furnace air until such time as the stove refractory temperature drops to such a low value that it must be reheated. Thus, at a given point in time, for a given blast furnace installation, some of the stoves are being heated by the passage of combustion products therethrough and the remainder of the stoves (heretofore usually only one) is serving to heat the blast air supply to the blast furnace. When the temperature of the heated air from a stove which is on blast drops to a predetermined value, a stove changeover is made at which time the flow of blast air through the stove which is on blast is curtailed and, at the same time, the flow of blast air through a previously heated stove is commenced.

Because the temperature of the heated blast air from a stove on blast drops continuously, due to the cooling effect exerted on the refractory by the air previously passed therethrough, and because of the fact that proper blast furnace operation requires minimal variation in the temperature of the air supply thereto, it has been customary to bypass could blast air around the stoves and to blend the heated air from the heating stove with bypassed air in such varying proportions as to maintain the temperature of the hot blast air, which is the mixture of heated air and cold bypassed air, at a relatively constant value.

In recent years there have been substantial changes in blast furnace operating practice, such as the more widespread use of beneficiated ore burdens, which make it desirable to supply hot blast air to the blast furnace at temperatures considerably in excess of the design capabilities of existing blast furnace stove installations. With respect to such existing installations it has been found that the heated blast air requirements of current blast furnace practice can be met at least expense by suitably modifying existing equipment to provide for simultaneous operation of two stoves at different outlet air temperatures in parallel. ln such a system, the correct hot blast air temperature is obtained by varying the relative rates of air ilow through the stoves which are on blast to provide a mixture of the correct temperature.

There were, however, two major problems which had to be overcome to permit parallel operation of two stoves in such a manner. First of all, it was necessary to substantially reduce the time required to heat a stove to a sufficiently high temperature to be put on blast. A substantial contribution to increased stove heating rates was provided with the introduction of the high mixing rate stove heating burner described in my copending US. patent application S.N. 154,596 tiled on November 24, 1961. Secondly, it was necessary to provide a hot blast temperature control system to control the relative rates of flow of blast air through the parallel stoves lCe on blast which would take account of the fact that an increase in blast air flow through a particular stove would increase the hot blast temperature when the temperature of the heated air from the stove was higher than the hot blast temperature and would decrease the hot blast temperature when the temperature of the heated air from the stove was lower than the hot blast temperature.

lt is toward the solution of this second problem that the present invention is directed. For a further understanding of this invention, attention is directed to the following portion of the specification, the drawing, and the appended claims.

ln the drawing:

FG. 1 is a schematic View of blast air heating apparatus embodying the present invention;

HG. 2 is a view which shows the output of each of the relay transmitters associated with the blast air temperature control system of FG. in relationship to the intensity of the control signal from the temperature controller;

EG. 3 is a graph which shows the time relationship of the temperature, T, of the blast air from the various stoves of a typical four stove installation, over one cornplete stove changing cycle;

FG. 4 is a graph which shows the time relationship of the ilow rate, Q, of heated blast air from the various stoves of a typical four stove installation, over the one complete stove changing cycle of FG. 3;

FIG. 5 is a fragmentary schematic view of a modilisation to the temperature control system for the apparatus of FIG. 1; and

HG. 6 is a view sirnilar to FlG. 2 which shows the output of the reversing relay transmitter associated with the blast air temperature control system of FIG. 5 in relationship to the intensity of the control signal from the temperature controller,

rlurning now to FIG. 1, there is illustrated a blast air heating system comprising a cold blast main 11, a hot blast main 12, and four blast air heating stoves F13-16. Blast air is supplied to the system at a constant rate, as by means of constant how fan 46 at the inlet of cold blast main 11.

Associated with each of stoves 13-16 are conduit means 1'?, comprising a cold portion 13 and a hot portion 1%, which serve to connect stoves 13-16 in parrallel to cold blast main 11 and hot blast main 12. The cold portion 1S of each of the conduit means 17 is provided with irst valve means 21, commonly called a cold blast valve; the hot portion 19 is provided with valve means 22, commonly called a hot blast valve; and conduit means 17 is further provided with additional valve means 23 comprising a flow modulating valve, preferably located in cold portion 18. Valves 21 and 22 are normally operated on a two-position basis, i.e., fully open and fully closed, and when both of valves 21 and 22 in a given conduit means are fully open, blast air will flow therethrough to be heated in the associated stove at a rate which is modulated by valve means 2-3. When valve 21 and 22 in the conduit means associated with a given stove are both open, the stove is in a condition known as Gn Blast and this invention is applicable in blast air heating systems having two stoves on blast simultaneously with one of the stoves being of a higher thermal content than the other, i.e., capable of heating the air passing therethrough to a higher temperature, as by not having been On Blast for as long a period as the other. In such a system, the stove which is at the higher thermal content is referred to as the Hot Blast Stove and the stove which is at the lower thermal content is referred to as the Cold Blast Stove. FIG. 1 illustrates a siutation occurring at a point in time dui'- ing the first Z1/2 hours of the stove cycle of FlGS. 3

and 4 wherein stove 14 is the hot blast stove and stove 13 is the cold blast stove. At the end of this period a new stove, stove 15, will become the Hot Blast Stove, stove 14 will become the Cold Blast Stove, and stove 13 will be taken off the On Blast condition.

After the thermal content of a given stove that has been On Blast has fallen to a predetermined low level, the stove is taken ott blast by closing valves 21 and 22 in the conduit means 17 associated therewith and by putting the stove in an On Gas condition. During periods when a stove is On Gas, its thermal content is raised to a higher level by passing the products of combustion of a fuel (usually blast furnace gas) from a burner 24 associated with each stove through the stove and out through an exhaust conduit 25 having a shutol valve 26, known as a chimney valve, which is open to flow only when the stove is On Gas. FIG. 1 illustrates a condition wherein stoves 15 and 16 are On Gas.

Since no heat is added to a blast stove during the On Blast portion of the cycle, the thermal content of the stove is continually reduced by heat transfer to the blast air passing therethrough. Thus, at the outset of the On Blast portion of the cycle, when the stove is Serving as a Hot Blast stove, the temperature of the heated blast air passing therefrom, as sensed by an air temperature recorder (ATR) 27 coupled to the hot portion of each conduit means 17, will be at a value somewhat higher than that desired of the blast air introduced into the blast furnace. Likewise, at the end of the On Blast portion of the cycle, when the stove is serving as a Cold Blast stove, vthe temperature of the air passing therefrom will be at a value somewhat lower than that desired of the blast air for the blast furnace. Because it is normally desired to maintain the temperature of the blast air to the blast furnace at a value within a relatively narrow predetermined range, it is necessary to continually vary the llows of blast air through the Hot Blast, and Cold Blast stoves to compensate for the fact that the thermal content of each of the stoves is continually decreasing.

The variation of the ilow rates through the stoves on blast is accomplished, ultimately, by the controlled manipulation of the modulating valve means 23, associated with each of the stoves which is On Blast. Thus, at any given time, for the system of FIG. 1, which, by way of example, is designed to provide a total of 90,000 s.c.f.m. (cubic feet per minute at standard conditions), the identity of the stoves which are On Blast and the temperature level of the air emerging from each can be ascertained by reference to FIG. 3 and the rate of ow, Q, through each of the stoves On Blast which will meet the prescribed conditions can be ascertained by reference to FIG. 4. For example, at a point in time hours after the initiation of the stove changing sequence, stoves and 16 will be in an On Blast condition with stove 16 serving as the Hot Blast Stove and stove 15 serving as the Cold Blast Stove. The temperature of the blast air from stove 16, T-16 will be approximately 1950 F. and the temperature of the blast air from stove 15, T-15, will be approximately 1430 F. To achieve the desired conditions of 90,000 s.c.f.m total ow at 1600 F. it is necessary to split the ow of blast air through stoves 15 and 16 such that the vilow through stove 15, Q-15, is approximately 60,000 s.c.f.m. and the flow through stove 16, Q-16, is approximately 30,000 s.c.f.m. As time progresses from the 5th hour both T-15 and T-16 will decrease and it will be necessary to increase ilow Q-16 and to equally decrease flow Q-16 in order to maintain a total flow of 90,000 s.c.f.m. at 1600 F.

The means for accomplishing the manipulation of the modulating valve means 23 in the desired manner comprises a blast air temperature recording controller (BATRC) 28, such as a Leeds & Northrup Speedomax G recording controller, adapted to transmit a control signal, preferably pneumatic, which varies in intensity from a low value to a high value depending on the deviation of the hot blast air temperature, as measured by a thermocouple located in the hot blast main at point 29, from a predetermined value. The output signal from controller 28 is connected to each of two transmitters 31 and 32 which, in a pneumatic system, are called sequence relays (SQR) and which may, for purposes of illustration, comprise Ratio Totalizers marketed by Hagan Chemical and Control, Incorporated, of Pittsburgh, Pennsylvania (the operation and function of which is described in Hagan bulletin 5452, copyright, Hagan Corporation, 1952), Standatrol Relays marketed by Bailey Meter Company, of Cleveland, Ohio, or Computing Relays marketed by The Foxboro Company, of Foxboro, Massachusetts. Interposed between the blast air temperature recorder and the transmitters 31 and 32 is manualautomatic selector switch (M/A) 44 which normally remains in the automatic position; however, it can be put into the manual position in which case an operator may manually control the signal to transmitters 31 and 32 independent of the control signal from controller 28. Also interposed between selector 44 and transmitters 31 and 32 is a solenoid timer (ST) 35, the function of which is explained later.

As is shown in FIG. 2 transmitter 31 is adapted to transmit a control signalV of a high intensity when the intensity of the signal transmitted thereto is at a high value and to transmit a control signal of a low intensity when the intensity of the signal transmitted thereto iS at a low value. Transmitter 32, on the other hand, performs a reversing function in that it is adapted to transmit a control signal of a low intensity when the intensity of the signal transmitted thereto is at a high value and to transmit a control signal of a high intensity when the intensity of the signal transmitted thereto is at a low value.

Associated with each of valve means 23 is an operator portion 33. Each operator may selectively be coupled to the output signal from transmitter 31 or to the output signal from transmitter 32 by switching means comprisi ing, illustratively, a switching valve 34 and a relay switching electric Valve operator (RSEV) 43 having three pod sitions, i.e., On Gas (G), On Blast-Hot (HB), and On Blast Cold (CB).

In instances where each valve operator 33 is adapted to position the associated valve means 23 for the maximum ow of blast air when the signal imposed thereon is minimal, the valve operator will be coupled to the output signal of transmitter 31 vwhen the associated stove is serving as a hot blast stove, and it will be coupled to the output signal of transmitter 32 when the associated stove is serving as a cold blast stove. Thus, in the apparatus of FIG. 1, therswitching means associated with stove 13, the Cold Blast stove, is positional to couple the associated valve operator 33 to the output signal from transmitter 32, and the switching means associated with stove 14, the Hot Blast stove, is positional to couple the associated valve operator to the output signal from transmitter 31. These positions are shown diagrammatically in FIG. 1 wherein the relay operator (RSEV) 43 associated with the stove 13 is shown in the Cold Blast, CB, position, and the relay operator (RSEV) 43 associated with stove 14 is shown in the Hot Blast, HB, position. Also the relay operators (RSEV) 43 associated with stoves 15 and 16 are shown in the On Gas, G, position. VThe consequence of this arrangement is that theow of blast air through the hot blast stove will be increased and the ow of blast air through the cold blast stove Will be decreased if the temperature sensed at point 29 decreases. The valve 23 of `each of the stoves 13, 14, 15 and 16 may also be manually operated at any time by switching manual-automatic selector (M/A) 45 associated therewith to the manual position.

FIG. 5 illustrates a modified temperature control system which requires only one transmitter 132 in addition to the transmitter which is a portion of controller 28. Transmitter 132 comprises, for a pneumatic system, a reversing relay which may also be a Ratio Totalizer by Hagan or one of the other noted commercial relays. As shown in FIG. 6, the output signal from transmitter 132 increases linearly from a minimum value to a maximum value (say 30 p.s.i.g.) as the output signal from controller 2S decreases from a maximum value to a minimum value (30-0 p.s.i.g.). As shown in FIGS. 5 and 6, this signal from transmitter 132 goes to switching valve 34 of stove 13 which will cause valve 23 associated therewith to close as the signal from transmitter 132 increases (as the temperature of the hot blast decreases). The signal from controller 28 is transmitted directly, through selector 44 and timer 35, to switching valve 34 of stove 14, and this will cause valve 23 associated therewith to open as the signal from controller 28 increases (as the temperature of the hot blast decreases).

The arrangement of FIGS. l and 2 is preferred over that of FIGS. 5 and 6 for the reason that it permits the valve means 23 associated with one or the other of the stoves that are On Blast to be maintained in the maximum flow position thereby minimizing the resistance of the system to the ow of blast air with an associated minimization of the horsepower consumed by the blast air blowers. This eect is obtained by arranging transmitter 31 to transmit a constant minimal signal (say 0 p.s.i.g.) for signal values from controller 28 in the lower portion (say 015 p.s.i.g.) of its range (say 0-30 p.s.i.g.) and by arranging transmitter 32 to transmit a constant minimal signal (O p.s.i.g.) for signal values from controller 28 in an upper portion (say 15-30 p.s.i.g.) of its range. Consequently, when the hot blast air temperature is such that the output signal from controller 23 drops in intensity over an increment in the range of -15 p.s.i.g., the valve means 23 associated with Cold Blast stove 13 will remain fully open and the valve means 23 associated with Hot Blast stove 14 will incrementally approach the open position. This change will have the effect of increasing the rate of blast air ilow through stove 14, Q-14, and decreasing the rate of blast air ilow through stove 13, Q-13, as shown in FIG. 4.

When vthe thermal content of the cold blast `st-ove drops to a predetermined low value, the stove is taken oi the On Blast condition and put in an On Gas condition by making the On Gas selection at its selector switch 34, by closing valves 21 and 22, and by opening valve 25, among other steps. In most situations the thermal content of the stove which has been in the hot blast condition will fall in the same period to such 4a low value tha-t the stove is no longer capable of serving as a hot blast stove. Thus, shortly before the cold blast stove is put On Gas, a third, recently heated, stove will be put into `a hot blast condition by making the On Blast-Hot selection at its selector switch, 'by closing its valve 26a and by opening its valves 21 and 22; and the stove previously on Hot Blas condition will Ibe changed to a Cold Blast condition by making the On Blast-Cold selection at :its selector switch 34.

At this time the signal from the transmitter of controller 2S will 4be of an intensity in the lower portion of its range thereby calling for a fully open position of the modulating valve 23 of the hot blast stove. It is desirable, however, to prevent a sudden rise in :the temperature at point 29 occasioned by the passage into hot blast main '12 of heated air from a hot yblast stove at considera-bly higher thermal content than that of the stove immediately preceding t in hot blast service at the time of the changeover. This may be accomplished by interposing a solenoid timer (ST) switching device in the output line from controller 28. Switching device 35 is adapted, when energized as by a contact (not shown) made when Valve 22 of the new hot blast stove is opened, to impose a signal of regulated intensity (say 30 p.s.i.g.) from a source, such as regulator 36, upon transmitters 31 and 32 for a prede- 5 termined time interval suicienftly long to allow controller 23 to acclimate itself to the changed condition-s.

As an added feature of the invention means Iare provided tt-o by-pass cold blast air from cold blast main 11 to hot blast main l2 during periods when :the thermal content of the stove which is Gn Blast-Cold is unusually high in order to keep the temperature of the hot blast air from exceeding a predetermined value. In the system of FIG. 1 the aforesaid means comprises a by-passv conduit 37 connecting cold Iblast main 11 to hot blast main By-pass conduit 37 is provided with a by-pass valve 38 which is normally in the closed position. Control means sensitive or responsive to the temperature of the hot `blast air are provided to open by-pas's valve 38 to keep the hot blast air temperature from exceeding -a predetermined value. Such control means may comprises for example, for a pneun atic system, a by-pass relay (BPR) 3@ coupled to the output signal from controller 28 and adapted to transmit a control signal to by-pass valve operator t1 which will cause operator to commence open- 'ng valve 3d when the output signal from controller 28 reaches a predetermined value (say 29 p.s.i.g.). This ast air by-pass feature can, of course, be incorporated in the `control system of FIG. 5.

As will be evident to those skilled in the art, various modifications can be made to the embodiments of this invention without departing from the spirit or scope of the invention as claimed hereinafter.

I claim:

1. A blast furnace air heating system comprising, in combination:

a cold blast main;

a hot blast main;

at least three heating stoves;

conduit means associated with each stove for connecting the stoves to the cold blast main and to the hot `blast main in parallel to each other;

first valve means in each conduit means adapted, when closed, to block the ilow of blast air from the cold blast main to the hot blast main through the respective conduit means, the r'irst valve means in the conduit means associated with two stoves being open to flow;

second valve means in each of said conduit means comprising a ilow modulating valve and a valve operator operable to position the flow modulating valve in response to a control signal;

temperature control means responsive to a condition indicative of the temperature of the hot blast air in the hot blast main for emittinf' a lirst control signal of an intensity from a low value to a high value;

a reversing transmitter responsive to a condition indicative of the temperature of the hot blast air in the hot blast main for transmitting a second control signal whose intensity is high when the intensity of `the first control signal is low and whose intensity is low whenthe intensity of the tirst control signal is high;

and switch means operatively associated with each of the valve operators for selectively making the operation o the valve operator responsive to one of the control signals when the associated stove is serving as a heating stove with a relatively high thermal content and responsive to lthe other of the control signals when the associated stove is serving as a heating stove with a relatively low thermal content.

2. Apparatus according to claim 1 and further comprising, in combination:

by-pass conduit means connecting the cold blast main to the hot blast main in parallel to the heating stoves;

normally closed valve means in the by-pass conduit means adapted, when closed, to block the ow of blast air through the bypass conduit means;

and control means operatively connected to said normally closed valve means and responsive to a conv.. 'a' dition indicative of the temperature of the hot blast air in the hot blast main for opening the normally closed valve means when said temperature exceeds a predetermined value.

3. Apparatus according to claim 2 wherein the control means comprises transmitting means responsive to one of said rst and second control signals.

4. Apparatus according to claim 1 wherein lthe reversing transmitter is responsive to said rst control signal and is adapted to transmit a second control signal which changes from a high value to a low value as the first control signal increases from a low value to an intermediate value and which remains at a low value as the iirst control signal increases from the intermediate value to ya high value and further comprising;

a transmitter responsive to said rst control signal for transmitting a third control signal which remains at a Ilow value as the rst control signal increases from a low value to an intermediate value and which increases from a low value to a high value as the rst control signal increases from the intermediate value to a high value, and wherein the switch means is adapted to selectively make the valve operator subject to one of the said second and third control signals when the associated stove is serving as a heating stove with a relatively high thermal content and to the other of the said `second and third control signals when the associated stove is serving as a heating stove with a relatively low thermal content.

5. Apparatus according to claim 4 further comprising means for substituting a regulated control signal in place of the first control signal for a predetermined interval of time following the operation of the switching means.

6. Apparatus according to claim 1 wherein said reversing transmitter is responsive to said irst control signal.

7. Apparatus according to claim 6 further comprising means for substituting a regulated control signal in place of the first control signal for a predetermined interval of time following the operation of the switching means.

References Cited by the Examiner UNITED STATES PATENTS 1,941,446 12/33 Isley 263--19 3,153,532 10/64 Touzalin 263-19 CHARLES SUKALO, Primary Examiner.

JOHN I. CAMBY, Examiner. 

1. A BLAST FURNACE AIR HEATING SYSTEM COMPRISING, IN COMBINATION: A COLD BLAST MAIN; A HOT BLAST MAIN; AT LEAST THREE HEATING STOVES; CONDUIT MEANS ASSOCIATED WITH EACH STOVE FOR CONNECTING THE STOVES TO THE COLD BLAST MAIN AND TO THE HOT BLAST MAIN IN PARALLEL TO EACH OTHER; FIRST VALVE MEANS IN EACH CONDUIT MEANS ADAPTED, WHEN CLOSED, TO BLOCK THE FLOW OF BLAST AIR FORM THE COLD BLAST MAIN TO THE HOT BLAST THROUGH THE RESPECTIVE CONDUIT MEANS, THE FIRST VALVE MEANS IN THE CONDUIT MEANS ASSOCIATED WITH TWO STOVES BEING OPEN TO FLOW; SECOND VALVE MEANS IN EACH OF SAID CONDUIT MEANS COMPRISING A FLOW MODULATING VALVE AND A VALVE OPERATOR OPERABLE TO POSITION THE FLOW MODULATING VALVE IN RESPONSE TO A CONTROL SIGNAL; TEMPERATURE CONTROL MEANS RESPONSIVE TO A CONDITION INDICATIVE OF THE TEMPERATURE OF THE HOT BLAST AIR IN THE HOT BLAST MAIN FOR EMITTING A FIRST CONTROL SIGNAL OF AN INTENSITY FROM A LOW VALUE TO A HIGH VALUE; A REVERSING TRANSMITTER RESPONSIVE TO A CONDITION INDICATIVE OF THE TEMPERATURE OF THE HOT BLAST AIR IN THE 